Carotenoids are organic pigments ranging in color from yellow to red that are naturally produced by certain organisms, including photosynthetic organisms (e.g., plants, algae, cyanobacteria), and some fungi. Carotenoids are responsible for the orange color of carrots, as well as the pink in flamingos and salmon, and the red in lobsters and shrimp. Animals, however, cannot produce carotenoids and must receive them through their diet.
Carotenoid pigments (e.g., β-carotene and astaxanthin) are used industrially as ingredients for food and feed stocks, both serving a nutritional function and enhancing consumer acceptability. For example, astaxanthin is widely used in salmon aquaculture to provide the orange coloration characteristic of their wild counterparts. Some carotenoids are also precursors of vitamin A. Also, carotenoids have antioxidant properties, and may have various health benefits (see, for example, Jyonouchi et al., Nutr. Cancer 16:93, 1991; Giovannucci et al., J. Natl. Cancer Inst. 87:1767, 1995; Miki, Pure Appl. Chem 63:141, 1991; Chew et al., Anticancer Res. 19:1849, 1999; Wang et al., Antimicrob. Agents Chemother. 44:2452, 2000). Some carotenoids such as β-carotene, lycopene, and lutein are currently sold as nutritional supplements.
In general, the biological systems that produce carotenoids are industrially intractable and/or produce the compounds at such low levels that commercial scale isolation is not practicable. Thus, most carotenoids used in industry are produced by chemical synthesis. There is a need for improved biological systems that produce carotenoids. Some efforts have previously been made to genetically engineer certain bacteria or fungi to produce higher levels of carotenoids (see, for example, Misawa et al., J. Biotechnol. 59:169, 1998; Visser et al., FEMS Yeast Research 4:221, 2003). However, improved systems, allowing higher levels of production and greater ease of isolation, are needed.